1. Field of the Invention
This invention relates to a tolan derivative as a novel compound and a liquid crystal mixture containing the same.
2. Description of the Related Art
Display elements having liquid crystals applied thereto make use of the electrooptical effect exhibited by liquid crystal substances, and the display modes thereof include various ones such as those of TN (Twisted Nematic) type, DS (Dynamic Scattering) type, guest-host type, DAP type, etc.
While the properties required for liquid crystal substances used vary depending on these respective modes, the following properties are required in common therewith:
a property that liquid crystal phases are exhibited within as broad a temperature range as possible and a property that the liquid crystal substances are stable to moisture, heat, light, air, etc. At present, however, there is no single compound which satisfies all of such requirements; thus there have been used liquid crystal mixtures obtained by mixing several kinds of liquid crystal compounds or mixing compound(s) similar to liquid crystal compounds with several kinds of liquid crystal compounds.
As to tolan derivatives used as a component of liquid crystal materials, compounds expressed by the following formulas (1) to (3) are disclosed in (1) French patent application laid-open No. 2,141,438, (2) Japanese patent application laid-open No. Sho 60-152427/1985 and (3) Japanese patent application laid-open No. Sho 60-204731/1985, respectively: ##STR2## wherein R.sup.3 and R.sup.4 each represent an alkyl group or an alkoxy group. ##STR3## and R and R' each represent a linear chain alkyl group.
These tolan compounds are liquid crystal materials having specific features of a large optical anisotropy value (hereinafter abbreviated to .DELTA.n) and a high clearing point.